2005 Tahoe Coolant level dropping
 

I have a relatively low mileage 2005 Tahoe that has never had a serious mechanical problem with the 5.3 liter motor. It has roughly 70 K miles. A few days ago my original DexCool level suddenly showed a pint drop in level in the reservoir. It had always been rock steady for 11 years since I purchased the vehicle new. I added new 50/50 mix and it has dropped again in less than 100 miles. There is no sign of external leakage anywhere. I initially expected maybe a water pump problem. I was actually hoping it was a water pump. I have done research and now fear internal leakage but I am not giving up on a less expensive problem. I notice the surge tank is pressurized. It has a 15 pound cap. When I open it it leaks some residual pressure (a slight flow or puff). Is this normal? Would my next checks be pressure checks of the system? Followed by maybe inspection of plugs for discolored plugs? I smell no antifreeze at all either cold or hot. The exhaust is colorless. I have never removed a plug before so I do not know their condition (If not broke, don;' fix it is my watch word) but here I am scratching my head. I have read postings on line about porous head castings in Duramax engines that once detected leaking should be replaced (I am beyond warranty so that is $$$$.) I have heard of people putting in the GM coolant sealing tablets and fixing their problem. At this point I am having visions of either fixing it with tablets which I have ordered on line, or replacing the surge tank cap (not sure why that might help) or selling it before it gets worse. Any one have any experience with this situation and any thoughts about steps to proceed?

Check your oil dip stick, not heard of a vortec doing this, but the 3.1, 3.4 was a common issue with lower intake manifold gaskets

No apparent sign of anything wrong on the dip stick (yet). I found another post about the possibility of loose head bolts on a 2000 vortec engine. 10-16 lb ft vs 22 spec. https://chevroletforum.com/forum/sil...-vortec-56887/ I am going to look for rf head casting number as my next step. I am taking this step wise and going from free approaches to more expensive. I think I said duramax engine but meant vortec in my original post. Also, as I understand it, the vortec has no coolant flowing in the intake manifold gasket area. Thanks for your response

Head casting number on my Vortec 5.3 L heads are 862 which are apparently better than a head casting of 706 which were problematic.. I will now see if the head bolts are a little loose.

Check the underside of the oil fill cap. Moisture or gray jell means water is getting to the innards of the engine. Might try Bar's Stop Leak. I've had good luck w/ it.

73shark, I have been monitoring for the tell tale moisture under the oil fill cap. There is nothing there which is good I suppose. I use synthetic oil and it is clean looking. I have not removed the valve covers yet as it was too cold and windy yesterday. Maybe I should go back to looking for a small external leak but it is such a minor leak that it is not showing up anywhere that I can see. I so want it to be an external leak. I am getting some GM antifreeze stop leak tablets today but I would prefer not using them if it an external leak that can be fixed relatively easily. As I do not have an accessible garage and I have a gravel driveway, It's the worst possible time of the year to have a problem like this. I might need to bite the bullet and take it to a mechanic to give it a good evaluation. I realize that it is near impossible for anyone to help unless there is some advice on where to look for an external leak since the possible internal leak is not really showing signs yet. Thanks for your response.

Coincidentally, I received a coupon for a discounted coolant flush from a local Chevrolet dealer so I decided to take it in today. I had the coolant flushed after first telling them of my coolant drop experience. They flushed the system and said everything looked good. I will determine if any coolant leaks down and continue to troubleshoot with the new coolant fill. They replaced the coolant with DexCool by the way as this was the original specification coolant. Fingers crossed.

A couple places to check, the heater hose connections at the fire wall, also the drivers side tank on the radiator(I've seen a few split on the front side of the tank)